Radio frequency (RF) power amplifier is a key component of radios that functions to convert a low power RF signal into a larger signal having significant power for driving, for example, the antenna of a transmitter. As more and more of the radio processing chain goes digital, there is currently great effort to digitize and integrate the PA, which traditionally was implemented off-chip with discrete analog components.
Considering digital radios, a key technical challenge of 60 GHz CMOS radios is poor efficiency of their power amplifier (PA). By using advanced digitally intensive transmitter architectures, such as outphasing and direct digital-to-RF conversion, a nonlinear switch-mode PA can be used to improve the total system efficiency. Switching power amplifiers, however, are rarely seen at mm-wave frequencies due to the large output capacitance and low current capability of CMOS transistors. In a prior art power amplifier, a two-turn inductor is exploited to realize a switch-mode PA at 60 GHz. This inductor, however, must be large enough to simultaneously satisfy the required reactance for both fundamental and second harmonics. Consequently, its relatively large inductance limits the output transistor size so the PA output power (Pout) is less than 10 dBm.
There is thus a need for a power amplifier that is suitable for integration with mm-wave 60 GHz CMOS based radios having wide bandwidth and high efficiency and generates sufficient output power.